Obstructive coronary artery disease is generally regarded as a serious health problem in the United States and most of the western world. When drug treatment fails or inadequately controls angina pectoris, coronary artery bypass graft surgery is generally used. In 1964 a translumenal coaxial catheter dilation method for dilating atheromatous lesions in peripheral arteries was introduced by Dotter and Judkins. This technique required sequential dilation of stenotic lesions and employed progressively larger dilating catheters. Subsequently in 1971 a "Fogarty balloon catheter" was used to perform translumenal arteriolplasty. Subsequently, Gruntzig employed earlier techniques using a single double lumen catheter with a nondistensible balloon segment at its tip which was positioned in the lumen at the stenotic segment of a peripheral artery. The elastic balloon segment was then inflated, resulting in compression of the atheromatous lesion in a manner perpendicular to the vessel, thus dilating the lumen. The balloon remained inflated for ten to fifteen seconds at seven atmospheres internal pressure and was then deflated. As a result, there was a significant reduction in complications due to endothelial damage, such as that caused by earlier known coaxial translumenal dilation technique and thus a marked improvement in vessel patency through the use of the Gruntzig catheter was achieved.
In earlier designs, the amount of pressure which could be applied through a balloon type expander was limited and thus insufficient to dilate certain stenotic lesions. This shortcoming was due to the use of polyvinylchloride balloons which had structural limitations that limited internal pressures to approximately seven atmospheres.
Other catheter designs resulted in a total cessasion of blood flow distal to the site of the treatment. Studies in living dogs with normal coronary arteries have shown that coronary translumenal angioplasty may be associated with brief, self-limited ventricular tachycardia. During the inflation of the balloon, distal coronary pressure falls to zero. Because of the lack of blood flow and the pressure distal to the treatment site the period of use such known catheters must be relatively short to prevent complications due to the lack of blood supply. This limitation on inflation time tended to reduce the success rate of the coronary translumenal angioplasty.
The translumenal coronary angioplasty technique consists of a catheter system introduced via the femoral artery under local anesthesia. A preshaped guiding catheter is positioned into the orifice of the coronary artery and through this catheter a second dilation catheter is advanced into the branches of the coronary artery. The dilation catheter had an eliptical shape distensible balloon portion near its tip which could be inflated and deflated. After traversing the stenotic lesion of the coronary artery, the distensible portion was inflated with fluid which compressed the atherosclerotic material in a direction generally perpendicular to the wall of the vessel thereby dilating the lumen of the vessel. Peripheral arterial lesions treated by this technique have demonstrated that the atheroma can be compressed leaving a smooth luminal surface. Studies have shown that the patency rate two years following the dilation of the iliac and femoropopliteal atherosclerotic lesions was greater than seventy percent.
Although guiding catheters are used in placement of angioplasty (dilation) catheters, the angioplasty catheter can be placed in a stenotic lesion using solely the wire guide if the lesion is proximately located to the point of entry in the body. The word "guide" as referred to in this application is directed to both wire guides and guiding catheters separately or as used in tandem. Typically a guide of appropriate size is advanced through the stenotic lesion and the balloon catheter is threaded over it and advanced to the area of the stenosis. Once the area of the stenosis is reached, the balloon in the catheter is inflated to a high pressure depending on the size of the balloon and the type of stenosis, and the pressure is held for a period of time. During the procedure the distal and proximal pressure is measured to evaluate the physiological conditions of the organ. More specifically, the pressure differential is measured after deflating the balloon and is used as an indication of the degree of dilation achieved.
Past designs have employed a stiff catheter tip on the angioplasty catheter which often resulted in pulling the guide out of the stenoic lesion as the catheter was advanced toward the lesion. Separately, in using the angioplasty catheter, it was often necessary to measure the pressure distal to the catheter. Past designs employed a guide closely fitting to the internal cross section of the distal lumen in the catheter thereby making it difficult to obtain adequate pressure measurements due to the large pressure drops involved as a result of the usage of close clearances. The pressure measurements were of the nature of a dynamic measurement, the accuracy and frequency response of which was greatly and adversely affected by the pressure drops within the catheter measurement lumen. It was frequently required that the guide be retracted and replaced in order to achieve accurate pressure measurement.
The use of angioplasty catheters often made it necessary to infuse drugs or oxygenated blood, distal to the stenosis to provide adequate physiological function of the organ in question. Past designs did not provide for such a separate lumen to carry drugs necessary to prevent undue contractions of the arterial wall as a result of the insertion of the angioplasty catheter. To the extent such drugs were necessary to relax the arterial wall, the lumen through which the guidewire passed served the auxillary function of a drug injection port. However, usage of the same lumen for pressure measurement as well as infusion of drugs or other fluids impeded the ability to maintain continuous and accurate pressure measurements.
Angioplasty catheters used in the past had relatively large catheter body diameters which tended to occlude the artery of concern causing reduced blood flow to the lesion or the organ it supplies. One such catheter is disclosed in U.S. Pat. No. 4,323,071 (FIG. 4). Other catheters although using a tapered body, employed a rigid tip which, if the arterial path was particularly tortuous, tended to pull the guide wire from the stenosis. One such catheter is disclosed in U.S. Pat. No. 4,413,989 (FIG. 8).
Flexible tips attached to the distal end of an angioplasty catheter have been used to inject radiopaque contrast or medicaments into the femoral artery as part of diagnostic or treatment procedures. Such deformable tips had the object of preventing punctures of the wall of the aorta and have been provided to have a larger cross-sectional profile than the catheter body to which they are attached. Some designs even featured means to inflate the deformable tip to increase the contact area between the tip and the body tissue to reduce the pressure per unit area applied to the tissue. One such design is disclosed in U.S. Pat. No. 4,531,943.
In past designs it was often difficult to estimate the location of the tip of the catheter. Prior designs employed the use of a gold band near the distal end of the catheter thereby making that portion of the catheter visible under an x-ray machine. However, because it was risky to attach such rings at the extreme distal end of the catheter, the extreme distal tip of the catheter was not visible under x-ray and often the physician performing the procedure had to guess as to its location. This shortcoming of past catheters has been addressed in the catheter of the present invention by the provision of a radiopaque tip.
Known angioplasty catheters have dilation balloons attached to the catheter body by adhesives or by heat sealing. Most often, these balloons are made out of polyvinylchloride or irradiated polyethylene. Polyvinylchloride balloons are normally solvent or adhesive bonded to catheter bodies of the same material and polyethylene balloons are adhesive bonded or heat shrunk to catheter bodies of the same material, or a blend of polyethylene and polypropylene, so as to obtain catheter body stiffness. Most such catheters have relatively stiff tips at their distal end which often causes the preplaced guide to be pulled out of the lesion area during catheter advancement in tortuous arteries as well as intimal damage. Known catheters also contain relatively stiff bodies to carry the balloon adjacent the distal end of the catheter. The stiffness of the catheter body continues in the area of the balloon up to the distal end of the catheter.
Known catheters contain balloon lumen bleed holes whereby air can be removed directly out of the balloon cavity and out of the catheter during the filling of the balloon. These additional lumens either in the form of small metal tubes or as a multilumen catheter tube, consumed valuable cross-sectional area of the catheter tube that otherwise could be used for other purposes such as pressure measurements.
Known catheter designs have employed an inner and outer tube wherein the outer tube contains the balloon as an integral portion thereof or a separate balloon which is bonded to the outer tube. The annulus between the inner and outer tubes is used for inflation of the balloon.
Known angioplasty catheters have been shipped in a sterilized condition to doctors and hospitals with the balloon in a deflated condition and having gas entrained therein. Prior to using such catheters, doctors or technicians had to inject a contrast fluid into the balloon to displace the gases therein. This procedure involved sequential filling and evacuation of balloon using a plunger connected to the proximal end of the catheter. Such catheters were shipped to doctors and hospitals with the balloon in a wing-folded condition. Essentially wing folding involved flatening of the balloon along the catheter body and folding the balloon over onto the catheter body in two segments which resemble wings coming from a fuselage. In the past, the catheters were wing-folded in the factory prior to shipment. However, in order to remove the entrained gases, the doctor or technician had to unfold the wings and fill the balloon with contrast fluid while evacuating gases therefrom. As a result, the advantage of the balloon tending to retain its wing-folded position after shipment was lost. The doctor or technician after filling the balloon with contrast fluid had to again attempt to manipulate the balloon with his or her fingers to reachieve the wing-folded position which reduced the profile of the catheter.
The catheter of the present invention addresses this problem by prefilling the catheter with contrast fluid and placing a sleeve over the balloon after it has been wing-folded. Accordingly, the advantage of the wing-folding is retained and the doctor merely removes the sleeve and the sterile catheter is ready for insertion, with the balloon in a low profile position.
It is an object of this invention to provide a soft atraumatic catheter tip in which radiopaque fillers such as bismuth-oxychloride or bismuth-subcarbonate are incorporated.
It is an object of the invention to provide a relatively soft catheter tip to minimize the tendency of the catheter to dislocate a guide out of a stenosis when the catheter is advanced in a tortuous path, and also minimize intimal damage.
It is another object of this invention to provide a catheter tip which can be insert molded, heat bonded, or adhesive bonded to the relatively stiff catheter body proximal to it. It is a further object of this invention to use material such as nylon, polyvinylchloride, polyurethane, of different stiffnesses that are readily bondable using the aforementioned methods.
It is a further object of this invention to provide an inner tube that is relatively large in its internal diameter and that is necked down in the region of the balloon and for several centimeters proximal to the balloon in order to provide a large lumen for pressure measurement. The catheter provides an improved frequency response without sacrificing the total overall outside diameter and maintaining a relatively small diameter in the region of the balloon thereby maintaining a low profile catheter design.
It is a further object of this invention in one of its alternate embodiments to provide a bleed lumen to bleed gases out of the balloon wherein the lumen extends within the wall of the outer tube thereby avoiding sacrificing any of the catheter cross-sectional area for other lumens thereby allowing such other lumens to be of maximum cross-sectional area within a low profile catheter.
It is a further object of this invention to provide, in one embodiment, an opening into the balloon cavity at its extreme distal end thereby facilitating the removal of gases during filling with contrast fluid.